1. Field
This art relates to an electric circuit device for supplying electric power to an internal circuit in a semiconductor circuit.
2. Description of the Related Art
Power source cut-off function is one of the functions for reducing power consumption of a semiconductor integrated circuit used for an electronic apparatus. The power source cut-off function is a function for stopping supplying power source to a particular block in an internal circuit that is in a standby state. Herewith, needless power consumption of the particular block that is in a standby state can be reduced to elongate the continuous operation time of the electronic apparatus.
In order to stabilize the operation of the internal circuit, a capacitor for stabilizing power source voltage is generally connected in parallel with the internal circuit. When the connection between the internal circuit and a power source is cut off, the connection between the capacitor and power source is also cut off at the same time. On the other hand, the internal circuit and the capacitor are always connected, so that when the connection with the power source is cut off, the electric charge of the capacitor is discharged by the internal circuit. Consequently, when the internal circuit and the power source are connected again, it is necessary to charge the capacitor. Consequently, the power source voltage is rapidly lowered to destabilize the operation of the internal circuit.
A technique has been known by which rapid power source voltage fluctuation is prevented when activating the internal circuit by gradually increasing the gate voltage of a MOS switch that connects the internal circuit and the power source when activating the internal circuit. The technique is disclosed in, for example, K. Fukuoka et al., “A 1.92us-wake-up time thick-gate-oxide power switch technique for ultra low-power signal-chip mobile processors”, Symposium on VLSI Circuits Digest of Technical Papers, pp. 128-129, 2007.